Predictive encoding of motion vectors including a flag notifying the presence of coded residual motion vector data

Abstract

The invention relates to a video encoding method applied to a sequence of video frames and generating a coded bitstream in which each data item is described by means of a bitstream syntax allowing any decoder to recognize and decode all the segments of the content of said bitstream. This method includes a predicting step, based on a prediction technique using a motion compensation operation, and a subtracting step, based on a subtraction of said predicted frame from the current one, and the motion compensation operation leads to motion vectors with horizontal and vertical components (MVx, MVy). These components have to be encoded differentially by using predictions (Px, Py) of said components and, in fact, only the differences (dx, dy) between the components and their predictions (Px, Py) are therefore encoded. According to the invention, said syntax includes an additional flag indicating that said differences (dx, dy) are present, or not, in the generated coded bitstream, and will have therefore to be decoded, or not, at the decoding side.

1 . A video encoding method applied to a sequence of video frames and generating a coded bitstream in which each data item is described by means of a bitstream syntax allowing any decoder to recognize and decode all the segments of the content of said bitstream, said method including a predicting step, based on a prediction technique using a motion compensation operation between a previous frame and the current one and provided for generating a predicted frame, and a subtracting step, based on a subtraction of said predicted frame from the current one and provided for generating the signal to be encoded, said motion compensation operation itself leading to the generation of motion vectors the horizontal and vertical components (MVx, MVy) of which have to be encoded differentially by using predictions (Px, Py) of said components and encoding only the differences (dx, dy) between said motion vector components and their predictions (Px, Py), said encoding method being further characterized in that said syntax includes an additional flag indicating that said differences (dx, dy) are present, or not, in said generated coded bitstream.  
     
     
         2 . A video encoding device for carrying out a video encoding method applied to a sequence of video frames and generating a coded bitstream in which each data item is described by means of a bitstream syntax allowing any decoder to recognize and decode all the segments of the content of said bitstream, said encoding method including a predicting step, based on a prediction technique using a motion compensation operation between a previous frame and the current one and provided for generating a predicted frame, and a subtracting step, based on a subtraction of said predicted frame from the current one and provided for generating the signal to be encoded, said motion compensation operation itself leading to the generation of motion vectors the horizontal and vertical components (MVx, MVy) of which have to be encoded differentially by using predictions (Px, Py) of said components and encoding only the differences (dx, dy) between said motion vector components and their predictions (Px, Py), said encoding device being further characterized in that said syntax includes an additional flag indicating that said differences (dx, dy) are present, or not, in the coded bitstream generated by said encoding device.  
     
     
         3 . A transmittable video signal consisting of a coded bitstream generated by a video encoding device for carrying out a video encoding method applied to a sequence of video frames and generating a coded bitstream in which each data item is described by means of a bitstream syntax allowing any decoder to recognize and decode all the segments of the content of said bitstream, said encoding method including a predicting step, based on a prediction technique using a motion compensation operation between a previous frame and the current one and provided for generating a predicted frame, and a subtracting step, based on a subtraction of said predicted frame from the current one and provided for generating the signal to be encoded, said motion compensation operation itself leading to the generation of motion vectors the horizontal and vertical components (MVx, MVy) of which have to be encoded differentially by using predictions (Px, Py) of said components and encoding only the differences (dx, dy) between said motion vector components and their predictions (Px, Py), said transmittable video signal being characterized in that said coded bitstream comprises a syntactic element in the form of an additional flag indicating that said differences (dx, dy) are present, or not, in said coded bitstream.  
     
     
         4 . A video decoding method for decoding a transmittable video signal consisting of a coded bitstream generated by implementation of a video encoding method applied to a sequence of video frames and generating a coded bitstream in which each data item is described by means of a bitstream syntax allowing any decoder to recognize and decode all the segments of the content of said bitstream, said encoding method including a predicting step, based on a prediction technique using a motion compensation operation between a previous frame and the current one and provided for generating a predicted frame, and a subtracting step, based on a subtraction of said predicted frame from the current one and provided for generating the signal to be encoded, said motion compensation operation itself leading to the generation of motion vectors the horizontal and vertical components (MVx, MVy) of which have to be encoded differentially by using predictions (Px, Py) of said components and encoding only the differences (dx, dy) between said motion vector components and their predictions (Px, Py), said decoding method being further characterized in that it comprises a step for reading in said coded bitstream an additional flag indicating that said differences (dx, dy) are present, or not, in said coded bitstream and have therefore, or not, to be decoded.  
     
     
         5 . A video decoding device for carrying out a video decoding method for decoding a transmittable video signal consisting of a coded bitstream generated by implementation of a video encoding method applied to a sequence of video frames and generating a coded bitstream in which each data item is described by means of a bitstream syntax allowing any decoder to recognize and decode all the segments of the content of said bitstream, said method including a predicting step, based on a prediction technique using a motion compensation operation between a previous frame and the current one and provided for generating a predicted frame, and a subtracting step, based on a subtraction of said predicted frame from the current one and provided for generating the signal to be encoded, said motion compensation operation itself leading to the generation of motion vectors the horizontal and vertical components (MVx, MVy) of which have to be encoded differentially by using predictions (Px, Py) of said components and encoding only the differences (dx, dy) between said motion vector components and their predictions (Px, Py), said decoding device being further characterized in that it comprises means for reading in said coded bitstream an additional flag indicating that said differences (dx, dy) are present, or not, in said coded bitstream and have therefore, or not, to be decoded.